diff --git a/examples/door-game/tests/test_world_loader.py b/examples/door-game/tests/test_world_loader.py
index 3eb7fdd8..02221394 100644
--- a/examples/door-game/tests/test_world_loader.py
+++ b/examples/door-game/tests/test_world_loader.py
@@ -828,3 +828,24 @@ def test_single_boss_accepted() -> None:
     bosses = [m for m in world.monsters if m.boss]
     assert len(bosses) == 1
     assert bosses[0].name == "the Wyrm Below"
+
+
+def test_overlapping_zones_rejected(tmp_path: Path) -> None:
+    """Overlapping zone rectangles are a load error.
+
+    ``zone_for`` returns the FIRST matching zone, so two zones sharing any cell
+    would silently shadow one tier band there — exactly the bug a cold-authored
+    pack shipped (a 1-column caldera-edge strip dropped to the low band). Pull
+    the deep zone west so its rect overlaps the near zone and confirm the loader
+    refuses it rather than loading the ambiguity.
+    """
+    pack = _clone_pack(tmp_path)
+
+    def mutate(data: dict[str, Any]) -> None:
+        for zone in data["zones"]:
+            if zone["key"] == "dungeon_deep":
+                zone["rect"][0] = 50  # now overlaps forest_near's x30..60 strip
+
+    _rewrite(pack / "world.json", mutate)
+    with pytest.raises(WorldLoadError, match="overlap"):
+        load_world(pack)
diff --git a/examples/door-game/understone/cli.py b/examples/door-game/understone/cli.py
index abbdd526..b11ffceb 100644
--- a/examples/door-game/understone/cli.py
+++ b/examples/door-game/understone/cli.py
@@ -385,29 +385,15 @@ def _render_validate_coverage() -> str:
     settings_count = len(loader.SETTINGS_BANDS)
     reserved = ", ".join(f"`{g}`" for g in _reserved_glyph_list())
     bullets = [
-        f"* **Economy and progression bands** — every one of the {settings_count} "
-        "`settings` fields must sit in its allowed range (the table above), and "
-        "`growth` must be present and non-negative.",
-        "* **Glyph safety** — every terrain, location, and legend glyph must render "
-        f"exactly one column and must not be a reserved marker ({reserved}).",
-        "* **Map integrity** — `width`/`height` in band, every `terrain_rows` row "
-        "exactly `width` long with `height` rows, and every row character in the "
-        "`legend`.",
-        "* **Walkability** — `spawn` and every placed location must sit on walkable "
-        "terrain (and no two locations share a cell).",
-        f"* **Display-name length** — every monster, item, and location name within "
-        f"`{loader.MAX_NAME_LEN}` printable characters; content lists within their caps.",
-        "* **The fight row** — `events.json` must hold at least one `fight` entry, "
-        "with weights `> 0`, `min <= max`, and amounts in their per-kind band.",
-        "* **Cross-references** — `legend` → terrain key, location placements → "
-        "`locations.json` keys, `starting_weapon`/`starting_armor` → item ids, "
-        '`boss_monster` → a monster flagged `"boss": true`, '
-        "`rare_drop_item` → a consumable item id, and `forge_ore_item` → a "
-        "`material` item id.",
+        f"* **Economy and progression bands** — every one of the {settings_count} `settings` fields must sit in its allowed range (the table above), and `growth` must be present and non-negative.",
+        f"* **Glyph safety** — every terrain, location, and legend glyph must render exactly one column and must not be a reserved marker ({reserved}).",
+        "* **Map integrity** — `width`/`height` in band, every `terrain_rows` row exactly `width` long with `height` rows, and every row character in the `legend`.",
+        "* **Walkability** — `spawn` and every placed location must sit on walkable terrain (and no two locations share a cell).",
+        f"* **Display-name length** — every monster, item, and location name within `{loader.MAX_NAME_LEN}` printable characters; content lists within their caps.",
+        "* **The fight row** — `events.json` must hold at least one `fight` entry, with weights `> 0`, `min <= max`, and amounts in their per-kind band.",
+        '* **Cross-references** — `legend` → terrain key, location placements → `locations.json` keys, `starting_weapon`/`starting_armor` → item ids, `boss_monster` → a monster flagged `"boss": true`, `rare_drop_item` → a consumable item id, and `forge_ore_item` → a `material` item id.',
         "* **Zone tiers** — every zone's tier band must overlap at least one monster tier.",
-        "* **Dungeon ladder** — every `dungeon_tiers` tier must have a non-boss "
-        "monster, and that tier's FIRST monster (its fixed rung guardian) must "
-        "not be `rare`.",
+        "* **Dungeon ladder** — every `dungeon_tiers` tier must have a non-boss monster, and that tier's FIRST monster (its fixed rung guardian) must not be `rare`.",
         '* **Exactly one boss** — at most one monster may carry `"boss": true`.',
     ]
     return "\n".join(bullets)
diff --git a/examples/door-game/understone/world/loader.py b/examples/door-game/understone/world/loader.py
index 4ad5a068..84f27ff4 100644
--- a/examples/door-game/understone/world/loader.py
+++ b/examples/door-game/understone/world/loader.py
@@ -579,6 +579,22 @@ def _decode_zones(
                 tier_hi=hi,
             )
         )
+    # Zones must not overlap: zone_for returns the FIRST match, so an overlap
+    # would silently shadow one zone's tier band on the shared cells. Reject it
+    # at load so an authored pack can't ship that bug unseen.
+    for i, first in enumerate(out):
+        for second in out[i + 1 :]:
+            if (
+                first.x0 <= second.x1
+                and second.x0 <= first.x1
+                and first.y0 <= second.y1
+                and second.y0 <= first.y1
+            ):
+                raise WorldLoadError(
+                    f"world.json zones {first.key!r} and {second.key!r} overlap; "
+                    "give each zone a distinct rectangle (zone_for takes the first "
+                    "match, so an overlap would silently shadow one tier band)"
+                )
     return out
 
 
diff --git a/examples/door-game/understone/world/packs/README.md b/examples/door-game/understone/world/packs/README.md
index 3887a6cf..ce730b8c 100644
--- a/examples/door-game/understone/world/packs/README.md
+++ b/examples/door-game/understone/world/packs/README.md
@@ -9,9 +9,9 @@ of the pack's JSON files). The slug is the subdirectory name. `understone
 worlds` discovers the Vale plus every pack here that carries a `world.json`,
 loads each one, and reports whether it is sound.
 
-The directory ships effectively empty (this README is the placeholder that keeps
-it under version control); alternate worlds are added here as they are authored.
-To serve one, point the server at it:
+This directory ships with one bundled alternate world — **The Cinder Wastes**
+(`cinder-wastes/`), an ashen volcanic underworld authored against `AUTHORING.md`.
+More are added here as they are written. To serve one, point the server at it:
 
 ```bash
 UNDERSTONE_WORLD=understone/world/packs/<slug> understone
diff --git a/examples/door-game/understone/world/packs/cinder-wastes/world.json b/examples/door-game/understone/world/packs/cinder-wastes/world.json
index b49bd9b2..22b7af0f 100644
--- a/examples/door-game/understone/world/packs/cinder-wastes/world.json
+++ b/examples/door-game/understone/world/packs/cinder-wastes/world.json
@@ -92,7 +92,7 @@
     },
     {
       "key": "caldera_deep",
-      "rect": [60, 8, 82, 22],
+      "rect": [61, 8, 82, 22],
       "tier_lo": 3,
       "tier_hi": 5
     }